Circuit-breaker system



Oct. 22, 1929. Q WES T 1,732,736

CIRCUIT BREAKER SYSTEM File Ap 12, 1928 2 Sheets-Sheet l BY ATTORNEYOct. 22, 1929. D. c. WEST CIRCUIQT BREAKER SYSTEM Filed April 12, 1928 2Sheets-Sheet 2 Millivolis on Relay Milamps DiNerence Between Coils lNVENTOR Donald C.West

AT1I'ORNEY Patented Oct. 22, 1929 warren STATES PATENT OFFICE DONALD C.WEST, OF EAST PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTING- HOUSEELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VANIACIRGUIT-BREAKER SYSTEM Application filed April 12, 1928.

This. invention pertains to an automatic reclosing-circuit-breakersystem, and, more particularly, to a system of the type described, inwhich the connection between a supply circuit and a load circuit iscontrolled by a circuit-breaker which is designed to'open automaticallyupon the occurrence of an over load or short-circuit on the loadcircuit, or in response to a manual operation, and to be automaticallyreclosed when the resistance of the load circuit increases to apredetermined value.

The principal object of my invention is to provide an automaticrcclosing circuitbreaker system whereby the resistance 01 the loadcircuit may be accurately measured to determine when the load circuitshould be reconnected to the supply circuit.

A further object of the system of my invention is to provide a reclosingcircuitbreaker system in which the resistance-measuring circuit is notset up until the lapse of a period of time, following the opening of thecircuit-breaker, that is sufi'icient to permit any transient conditionsresulting from the opening of the breaker to disappear. By this means,it is possible to prevent false OP. eration as a result of the transientconditions that follow the interruption of a heavy current in adistribution system.

A further object of my invention is to pro vide a system of the typedescribed which shall be entirely unaffected by variations in thevoltage of the supply circuit.

A still further object of my invention is to utilize a galvanometerrelay to cause a resistmice-measuring circuit to be connected so as tomeasure the resistance of the load circuit when the circuit-breaker hasbeen opened in response to any of the above-men tioned conditions, andto employ the same relay, in combination with the resistancemeasuringcircuit, to determine when the resistance of the load circuit hasincreased to definite predetermined value at which it is safe toreconnect the load circuit to the supply circuit.

In accordance with my invention, I utilize an inductively dampedgalvanometer relay of the D'Arsonval type to cause suitable re- SerialNo. 269,492.

sistors to be connected in the form of a VVheatstone bridge, of whichthe load circuit is one arm. By employing an inductively dampedgalvanometer, I introduce a time delay be tween the opening of thecircuit breaker and the setting up of the lVheatstone bridge circuit.Obviously, it may be desirable to employ an additional relay to obtainthe time delay between the opening of the circuitbreaker and the settingup of the resistance measuring circuit, but in the preferred embodimentof my invention, use is made of the time delay inherent is agalvanometer relay. It is, therefore, impossible for the circuitbreakerin the system of my invention to be reclosed as a result of transientconditions before the resistance of the load circuit has actuallyincreased to a safe value. This re lay is so designed that its movingelement,

when energized by current of a given polarity, magnitude and duration,is actuated first in one direction to set up the resistanceaneasuringcircuit in the nature of a lVheatstone bridge, and after setting up thelVheatstone bridge circuit, is so connected as to be responsive to thepotential between two diagonally opposite points of the bridge. Theresistors composing the bridge are adjusted so that, when the resistanceof the load circuit has increased to a predetermined value, whereby thebridge is balanced, the potential impressed upon the relay is zero. Therelay can be so adjusted that it will cause the circuit-breaker to bereclosed, to connect the supply circuit to the load circuit, when thepotential impressed on the relay is zero or when it has a definitepredetermined value of either polarity.

In a practical embodiment of my invention, the galvanometer relay is setto close its back contact member, to cause the circuit breaker toreclose, when the moving coil of the relay is entirely tie-energized asa result of the exact balancing of the VVheatstone bridge. Thus, Iobtain the full benefit of the extreme accuracy of the lVheatstonebridge method of measuring the resistance of the load circuit. Moreover,such a measurement is independent of the applied measuring voltage.

For a full explanation of my invention, reference is made to theaccompanying drawings, in which:

Figure 1 is a diagram illustrating the apparatus and circuits involvedin a preferred embodiment of my invention,

Fig. 2 is a schematic diagram of a portion of the circuit shown in Fig.1,

Fig. 3 is a set of curves illustrating the operation of the system of myinvention. Fig. 3 is a schematic diagram of the circuit, thecharacteristics of which are shown by the curves in Fig. 3,

Fig. 4 is a similar set of curves illustrating the operation of asystem. which has been widely used heretofore, Fig. 4 shows a differenttype of resistance-measuring circuit, the characteristics of which areshown in Fig. 4.

Referring to Fig, 1, the systemof my invention is designed to controlthe connection between a supply circuit and a load circuit 11 Thesecircuits are adapted to be connected by a circuit-breaker 12. Abridgingresistor 13is connected across the terminals of thecircuit-breaker 12 to form a part of the resistance-measuring circuit tobe described later.

A direct-current relay 14 of the DArsonval galvanometer type is employedto control the operation of the circuit-breaker 12. The magnetic circuitof the relay 14 may be either that of a permanent magnet or of anelectromagnet as shown, the exciting coil 15 of which is connected inseries relation with a resistor 15 across the supply circuit 10 and acommon return conductor 16; The moving coil 17 of the galvanometerrelayis connected to'one terminal of a resistor 18, the other terminalof which is permanently C011? nected to the supply circuit 10, and thecoil 17 is further connected through a currentlimiting resistor 19 to aresistor 20. The resistor 20 is adapted to be connected to the returncircuit 16 through. a back contact member 21 on a relay 22 and-abackcontact member 23 on the main circuit-breaker 12.

An overload relay 25, having its actuating coil connected in supplycircuit 10 and having a cont-act member 26, is provided for opening themain circuit-breaker 12, in a manner to be described later, on the.occur? rence of a short-circuit or overload.

In addition to the relays 14 and 22, I also make use of a relay 34 tocontrol the operationlof the circuit-breaker 12. The remaining detailsof the apparatus and circuits of the system of'my invention will be setforth in the course of the description of the method of operation, whichwill now be outlined.

Under normal conditions the circuitbreaker 12 is closed and the supplycircuit 10 is directly connected to the load circuit 11, the resistor 13being thus shortcircuited. The operating coil of the relay 34 isenergized, as a result of certain operations to be described later, andits contact members 35, 36 and 37 are closed, the latter serving tomaintain the circuit from the conductor 10 through the resistor 34, thecoil of the relay 34, the contact member 37 and thence to the conductor16.

The circuit for the operating coil 38 of the main circuit-breaker 12extends between conductors 10 and 16 and-includes the con tact member 35of the relay 34 and a current-limiting resistor 39.

The contact. member 36 maintains a shortcircuit across the terminals ofthe oporatin coil. of the relay 22 to prevent actuation of the contactmembers of the relay until the relay 34 is de-energized in a mannerabout to be described.

Upon the occurrence of an overload or short-circuit on the load circuit11, the overload relay is energized sufficiently so that it closes itscontact member 26. The closing of the contact member 26 short-circuitsthe operating coil of the relay 34, which is thereupon de-energized andcaused to open its contact members 35, 36 and 37. The opening of thecontact member 37 interrupts the previously-traced circuit including thecoil 34. The opening of the contact member interrupts the circuitincluding the closing coil 38 of the circuit-breaker 12whicl1 isthereupon permitted to open, to disconnect the load circuit 11 from thesupply circuit 10. Under these conditions the resistor 13 is connectedbetween the circuits 10 and 11 and the auxiliary switches 23 and 43ofthe main circuit-breaker are closed.

The opening of the contact member 36 of the relay 34 removes ashort-circuit from across the terminals of the operating coil of therelay 22, while the closing of the contact member 43 sets up a circuitfrom the supply circuit 10 through a current-limiting resistor 44 to theoperating coil of relay 22. This circuit is completed by the operationof the relay 14, in a manner to be described hereinafter.

The closing of the contact member 23 on the main circuit-breaker 12completes a circuit from the supply circuit 10 through the resistor 18,the moving coil 17 of the relay 14, the resistors 19 and 20 and thencethrough contact member 21 of the relay 22 and the auxiliary switch 23 tothe return circuit 16. lVl'ien the coil 17 of the relay 14 is thusenergized, the relay operates to engage its front contact member 45,after aslight time delay effected by inductive damping means integralwith the moving element of the galvanometer relay.

This time delay, as previously explained, permits the transientconditions set up in the distribution system by the opening of thecircuit-breaker 12' to disappear so that false operation of the relay 14to reclose the circuit breaker as a result of such conditions, will notoccur.

The closing of the front contact member 45 of the relay 14 completes thecircuit from the operating coil of the relay 22 to the return circuit16, and the relay 22 thereupon operates to close its contact members 46,47 48 and 49 and to open its contact member 21. The opening of thecontact member 21 interrupts the previously traced circuit includ ingthe moving coil 17 of the relay 14.

Simultaneously, the closing of the contact member 46 completes a lockingcircuit for the relay 22 to the return circuit 16. The closing oi thecontact member 47 connects the operating coil of the relay 34 to theback contact member of the galvanometer relay 14. This contact member isclosed in response to circuit conditions which will be described later.The closing of the contact member 48 connects the resistor 18 to aresistor 51 which is permanently connected to the return circuit 16, andthe closing of the contact member 49 connects the resistor 19 to theload circuit 11.

When the operations just described have taken place, it will be foundthat the re sistors 13, 18 and 51 are so connected. that they form, withthe load circuit, a V heatstone bridge, to two opposite corners of whichthe supply-load circuit 1016 is connected. To the other two corners themoving coil oi the galvanometer relay 14 is connected, in seriesrelation with the protective resistor 19. This scheme of connections maybe plainly seen in F It is obvious that, by proper selection of thevalues of various resistors, it will be possible to cause the movingcoil of the galvanometer relay 14 to be Clo-energized when theresistance of the load circuit attains a predetermined value. hen thiscondition obtains, the back contact member 50 of the relay 14 is closed,and a circuit is completed from the supply circuit 10 through resistor34, the operating coil of the relay 34, the contact member 47 of therelay 22, the contact member 50 of the relay 14 and thence to the returnconductor 16. The relay 34 is thereupon operated to close its contactmembers 35, 36 and 37.

The inductive damping means Which delays the engagement of the movincontact member of the relay 14 with the trout contact member 45, is alsoeffective to delay the engagement of the moving contact member with theback contact member 50. Thus an interval is provided in which thecircuit conditions may become stabilized, both immediately after theopening of the breaker and immediately preceding the reclosure thereot.

The closing of the contact member 35 reestablishes the previously tracedcircuit through the closing coil 38 of the circuitbreaker 12, but theresistor 39 is sho t circuited by a contactor 52, which is closed by theoperation of a relay 53 as a result of the closing of the contact member48 on the main circuit-breaker 12. The circuit for the relay 53 extendsfrom conductor 10 through contact member 43, the resistor 53, the coilof relay 53, and thence to the return circuit 16. When the maincircuit-breaker 12 is closed in response to the energization of the coil38, the relay 53 is de-energized and opens its contact member 52 toinsert the resistor in series relation with the closing coil 38 of thecircuitbreaker 12, in order to reduce the current in coil 88 to a safecontinuous value.

The closing of the contact member 36 of relay 34 short-circuits theoperating coil of relay 22, as previously described, which is thereupon(lo-energized to open its contact members 46 to 49 and to close thecontact member 21. The closing of the contact member 37 completes alocking circuit for the coil of relay 34, as previously set forth.

It will thus be observed that, in this preterred form, I provide meansfor automatically causing the opening of a circuit-breaker connecting asupply circuit to a load circuit, upon the occurrence of certainconditions. At the expiration of a predetermined operating period ortime after the opening of the circuit-breaker for any reason, the systemof my invention sets up a WVheatstone bridge resistance-measuringcircuit, whereby the resistance of the load circuit may be measured, andcauses the reclosing of the main circuitbreaker only when the resistanceof the load circuit increases to a predetermined value at which it issafe to reconnect it to the supply circuit.

I am aware that it has been proposed previously to employ a VVheatstonebridge in connection with an automatic reclosing circuit-breaker, butthe system of my invention entails numerous advantages over any suchsystems known heretofore.

By employing a galvanometer relay which has an inherent time delay inits operation, I am enabled to introduce a time delay between theopening of the circuit-breaker and the setting up of theresistance-measuring circuit. This method of operation prevents thereclosing of the circuit-breaker in response to an operation of theresistance-measuring circuit resulting from transient conditionsexisting in the distribution circuit as a result of the opening of thebreaker. According to my invention, the breaker is opened upon the occurren cc of a. short-circuit, and a time interval is introduced inwhich the circuit conditions become stabilized, before the re tance-m asuring circuit is connected to measure the resistance of the loadcircuit.

Another advantage of the system of my invention resides in the fact thata single relay and a single operating coil thereof function to controlthe setting up of the resistance-measurin g circuit, as well-as tocontrol the reclosinc; of the circuit-breaker when the resistance of theload circuit has increased to a predetermined value. It is obvious that,should there be a failure of the relay coil or contact members. theresistance-measuring circuit would. not be set up, and reclosing of thecircuit-breaker would be thereby prevented. In other words, theoperation of the relay to set up the rcsistance-measuring circuit teststhe relay and proves that it is in condition to measure the resistanceof the load circiut.

In the systems heretofore known, the accuracy of the resistancemeasurements depends on the resistance of the resistor bridging thecontact member of the circuit-breaker. Because of the inherent accuracyand sensitivity of the galvanomet-er relay, the system of myinventionpermits the use of a bridging resistor oi higher value thanthose employed in former systems, so that the transfer of current fromthe supply circuit to the load circuit is a minimum. This, of course, isa desirable condition from an operating standpoint.

While the lWhcatstone-bridge circuit has been suggested heretofore, ithas never been applied for practical operation because a relay of propercharacteristics for the purpose, namely, a relay of very highsensitivity combined with ruggedness of construction and permanence ofcalibration, has not previously been employed. The galvanonietcr relaywhich is employed in my system meets these requirements and has asensitivity so great that even though the resistor 19, which isconnected in series therewith for protection, is of considerable value,the resistance measurements can be made with very great accuracy.

As already pointed out, in the reclosing .1; "stem described herein thesame relay which, after a time delay following the opening of thecircuit-breaker, up a resistancen'icasuring circuit, also tunctions tocontrol the reolosing of the circuit-breaker when the I'GnlStflllCG ofthe load circuit has increased to a sate value. This system posses esthe advantage that reclosing oi the circuit-breaker before theresistance of the load circuit has increased to a safe value ispositively prevented, and, at the same time, when the rescnce ot' theload circuit has increased to a 'crn'iinod value, the circuit-breaker isvely recloscd, and the load circuit is reto service. The system of myinvenliltely to prevent reclosing when the resistance the load circuithas reached a safe value tl an the systems heretofore known. Thus, t esystem of my inventioncauses the cir i. turtaer advantage of the systemof my inventum is that its operation is entirely indcpcndent oi:variations in the voltage of the supply. circuit. This advantage resultsfrom the fact that the balancing of the lVheatstone bridge depends onlyupon the increase in the resistance of the load circuit and is in no wayaffect-ed by changes in the, voltage of the supply circuit.

This characteristic of the system oi my invention may, perhaps, be bestunderstood by a consideration ot'the curves shown-in Fig. These curvesillustrate the variation of the current through the winding of the relay1? with variations in the resistance of the load circuit. The curves A,B and C illustrate, re spectively, the variation in the relay current asa result of variations in the load resistance for different linevoltages, for example, 500, 600 and 700 Volts. As already indicated, therelay is may be adjusted to close its back contactmember at'a-ny desiredvalue oi? current through the moving coil 17. in. practice 1 ind it mostdesirable to adjust the relay so that its back contact member will beclosed when the current in the coil 17 is substantially Zero.

As shown. by the curves in Fig. 3, the current in the coil 17 of therelay is zero at a bed value of resistance in the load circuit, gardlcssoiithe value of the line voltage. it the relay is set. to close its backcontact member at acurrent value other than zero, it will be obviousthat variations in the line voltage will cause considerable variationsin the resistance of the load circuit at which the relay will close itsback contact member to cause the reclosing of the main circuitbreaker.This range of variation increases with thevalue of the current which therelay is set toclose its back contact member. It is desirable,therefore, to adjust the relay to close its back contact member at Zerocurrent inthe relay winding or as near to that condition as is possible.

Fig. 8 illustrates schematically the circuit shown in Figs. 1 and 2, thecharacteristics of which are illustrated by the curves of 3.

In Figsd and e I have shown the characteristics and the circuit of areclosing ein which has been used heretofore. In this system thereclosing oft-he circuit-breaker depends upon the eXistence of apredetermined diii'erence in the current-sin the opposing windings 60and Glof abalanccd relay Because of the inherent inaccuracies in thistype of instrument, it is possible to obtain a closure of its contactmember (not shown) only whenthe difference in the currents in theopposing coils is of a value within a fixed range. Thus, referring toFig. l, the relay 62 may operate when the difference between thecurrents in the coils 60 and 61 has a value greater than OE or less thanOF. The curves G, H and J illustrate the operation of the relay 62 atvarious values of line voltage, for example, 500, 600 and 700 volts.

Since the relay 62 may operate at any current diiierence having a valuebetween OE and OF, then, if the voltage of the system varies between 500and 700 volts, it is obvious that relay 62 may cause the maincircuitbrealzer to reclose at any value of resistance between OK and UL.

It will be apparent from a comparison of Figs. 3 and -41 that theaccuracy of the system of my invention is vastly greater than that oisysten'is heretofore known, an example of which is shown in Fig. 4. Thisincreased accuracy results largely from the inherent characteristics ofthe galvanometer relay and the extreme sensitiveness of the VVheatstonebridge as a resistance-measuring circuit.

As already stated, the accuracy with which the system of my inventionmeasures the resistance of the load circuit is very great over an almostunlimited range, so that by suitable adjustment of the various elementsof the circuit, the reclosing of the main circuit-breaker may beprevened until the actual resistance of the load has increased to a safevalue, whereupon the reclosing of the circuit-breaker is immediatelyeilected.

Inasmuch as various changes and modifications will appear to thoseskilled in the art, I do not wish to be limited to the exact embodimentof my invention herein shown and described except as indicated in theappended claims.

I claim as my invention:

1. A reclosing-circuit-breaker system comprising a circuit-breakercontrolling the con nection of a supply circuit to a load circuit, meansfor opening said circuit-breaker and means for reclosing thecircuit-breaker when the resistance of the load circuit has increased toa predetermined value, said means including a relay for setting up aWhea-tstonebridge circuit when energized by current in one direction asa result of the opening of the circuit-breaker and for causing thebreaker to reclose when the \Vheatstonebridge circuit subsequentlyapproaches a balanced condition, whereby the energization of the relayis reduced.

2. In a reclosing-circuit-breaker system,the combination with acircuit-breaker for controlling the connection of a supply circuit and aload circuit, and means for opening the circuit-breaker underpredetermined conditions, of a galvanometer relay for controlling thereclosing of the circuit-breaker when the resistance of the load circuitattains a predetermined value, said relay having a contact memberadapted to be closed when the relay is energized by current in onedirection to set up a WVheatstone-bridge measuring circuit and a secondcontact member adapted to be closed when the energization of the relayreaches a predetermined value, as a result of the substantial balancingof the bridge, to complete a circuit for causing the reclosing of thecircuit-breaker.

3. In a reclosing-circuit-breaker system, a circuit-breaker forconnecting a load circuit and a supply circuit, means for opening saidcircuit-breaker and a heatstone-bridge circuit for measuring theresistance of the load circuit, a galvanometer relay adapted to beconnected in said bridge circuit, having a contact member adapted to beclosed after a time interval when the relay is energized by current in agiven direction, and a second contact member adapted to be closed whenthe energization of the relay reaches a predetermined value as thebridge becomes substantially balanced, means connected to the firstnamedcontact member for setting up the \Vheatstone-bridge circuit, and meansconnected to said second contact member for cuit has increased to apredetermined value,

whereby the bridge is approximately balanced and the energization of therelay reduced.

5. A circuit-breaker system comprising a supply circuit and a loadcircuit connected by a resistor, a circuit-breaker for connecting saidcircuits directly, additional resistors and a galvanometer relay forcausing said resistors to be so connected as to form a Wheatstonebridge, one arm of which is constituted by said load circuit at adefinite time after the circuit-breaker is opened, and for causing thereclosing of the circuit-breaker when the resistance of the load circuitis increased to a predetermined value, whereby the bridge is balancedand the energization of the relay is changed.

6. A system for controlling the operation of a circuit-breaker adaptedto connect a supply circuit to a load circuit comprising a plurality ofresistors and a galvanometer relay for causing said resistors to beconnected in the form of a IVheatstone bridge of which the load circuitis one arm, at a definite time after the opening of the circuit-breaker,the supply circuit being connected to two opposite corners of the bridgeand the relay to the re maining corners, whereby the resistance of theload circuit is measured, and, when it attains a predetermined value,the bridge is balanced and the energization of the relay is changed, andmeans for causing the circuit breaker to be reclosed when theenergization of the relay reaches a predetermined value.

7. A circuit-breaker system comprising a supply circuit and a loadcircuit adapted to be connected by a circuit-breaker, means for openinsaid breaker, a plurality of resistors adapted to be connected to thecircuits to form a lVheatstone bridge of Which the load circuitcomprises one arm, and a galvanometer relay connected to said resistorsfor causing, them to be so connected at a definite time after theopeningof said breaker and for causing the circuit breaker to reclosewhen the energization of the relay is altered as the resistance of theload circuit increases to a predetermined value, dependent on the valuesof said resistors, at Which the bridge is approximately balanced.

8. In a reclosing-circuit-breaker system, a circuit breaker forcontrolling the connection of a load circuit to a supply circuit, anoverload relay and an auxiliary relay for opening said circuit breaker,the coil of the auxiliary relay being normally connected across thesupply circuit and adapted to be short-circuited by the operation of theoverload relay, a galvanometer relay having its operating coil connectedacross the supply circuit by the opening of said circuit breaker, asecond auxiliaryrelay having an operating coil connected to a contactmember of said galvanometer relay, for setting up a lVheatstone-bridgecircuit and connecting the galvanometer relay thereacross, the coil 01said first-mentioned auxiliary relay being also connected to a secondcontact member of said galvanometer relay, and a closing coil for saidcircuit breaker, normally connected across the supply circuit andadapted to be disconnected therefrom by the'first-mentioned auxiliaryrelay upon the de-energization of the latter.

In testimony whereof, I have hereunto subscribed my name this llth dayof April 1928.

DONALD C. VEST.

